そう言えば

The phrase そう言えば can be used at the beginning of a sentence to mean something like "that reminds me", or "now I remember." The person saying it has been reminded of something, based on remarks from the other speaker in the conversation.

Ａ：今日、田中さん、クラス休んだね。
Ｂ：そう言えば、昨日、お腹が痛いって言ってたよ。病気かもしれないね。
A: Tanaka-san skipped class today.
B: That reminds me - yesterday, he said his stomach hurt. He might be sick.

Ａ：ねえ、あの人、どこかで見たことない？
Ｂ：そう言えば、昔、どこかで会ったことがあるような気がする。
A: Hey, have you seen that person somewhere before?
B: Now that you mention it, I have a feeling that I met them somewhere a long time ago.

リー：おい、キチンで猫がいるんだよな。
アリス：ええ、新しい猫だよ。そう言えば、昨日子猫を見つけたんだ。
Lee: Hey, there's a cat in the kitchen.
Alice: Yeah, it's our new cat. That reminds me, I found her kitten yesterday.